I don't know much about Betsy DeVos, but I'm familiar about the clan she married into. Her father-in-law was a cofounder of Amway, one of the biggest multi-level marketing firms in the country; they make good stuff, but the money is made by recruiting other salesmen more than actual selling their products. Her husband Dick got the GOP nomination for governor in 2006 and lost.
They've been Republican party regulars for years, and Betsy has been an advocate of conservative school reform, encouraging charter schools (my sister helps runs a charter school here in Midland) and vouchers. The pick thus both gives conservative reformers a bone and gives an establishment Republican a slot as well as giving him an extra woman to give Mr. "grab them by the [crotch]" some coed diversity.
It also give the usual suspects on the left some good anti-corporate digs, letting them bash Amway and Blackwater, for it was Betsy's brother who helped found the security firm that became the biggest target of the left during the Dubya years this side of Halliburton.
Nikki Haley provides Trump with a good cop at the UN, a daughter of Sikh Indian immigrants who rose to become governor of South Carolina, winning over one of the redneckiest states in the union. She doesn't have much foreign policy credentials other than a few trade-oriented overseas trips as governor, but she provides a diplomatic counterweight to the nativist and misogynistic streaks in the administration. While the Indian government won't roll over and gush over her appointment, her ethnic background should help any low-post innovations to Obama's Asian Pivot. It also shows a degree of inclusiveness; not as much as a black of Hispanic nominee would, but still helpful.
She's also not an early Trump adopter, having been a Marco Rubio supporter in SC's early primary, so this also throws a bone to more traditional Republicans. She and Trump had a few exchanges of urinary products during the campaign, but this is kiss-and-make-up time, it would seem.
Having a John Bolton-type in the job might be fun for conservatives, but if you actually want to get some diplomacy done, having a more diplomatic person on the case could help. Trump has the bad-cop part down cold, so he needs a good cop like Haley to close the deal after he gets into a tweet war with other world leaders.
The early picks for Trump have blended establishment types like Priubus (hey, spelled it right the first time) and early-Trump-adopters like Bannon and Sessions. These two are in the former, although Haley came in as a Tea Party person against the SC establishment.